A radar image of asteroid 2005 YU55, which would trigger a 7.1-magnitude earthquake were it to collide with Earth. NASA/Cornell/Arecibo

November 3, 2011

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At about 6:30 p.m. EST next Tuesday, a large asteroid traveling more than 30,000 miles per hour will streak quite close to Earth — marking the nearest fly-by of any such asteroid in 35 years. But don't worry — it's not going to hit us. Four key questions:

How big is it?At its widest point, the spherical object, named 2005 YU55, is 1,300 feet across. That's a bit longer than four football fields, or about the length of an aircraft carrier. It will speed by us at a rate of nearly 9 miles per second.

How close is it coming?The asteroid will come within roughly 200,000 miles of Earth — or about 85 percent of the distance between the Earth and the moon. The asteroid's flight marks its "closest encounter with Earth in at least the last 200 years," says Eyder Peralta at NPR. Another asteroid this big won't fly by again until at least 2028.

So nothing to worry about, right?"Everybody can relax," says Mike Wall at Space.com. "The space rock is not going to slam into Earth." The relatively close approach should be looked at as a good thing, as it will allow scientists to study the asteroid and "predict the space rock's orbit even further into the future."

But what if it did smash into us?Such an impact would release a 71 mph blast of air strong enough to shatter windows 60 miles from the point of impact, while triggering a 7.1-magnitude earthquake that would create rippling tsunami waves up to 70 feet high. "But again, just to be clear, the asteroid ain't gonna hit us," says Dan Vergano at USA Today.